Method for generating a noncondensible gaseous fluid compatible with interhalogen oxidizers using phosphonitrilic chloride

ABSTRACT

Phosphonitrilic chloride (PNCl2) and polymers thereof are hypergolic with interhalogen oxidizers. The gaseous products of this reaction are insoluble in and nonreactive with liquid interhalogen compounds and are suitable for use as the pressurizing media for oxidizer expulsion systems in rocket motors.

United States Patent 91 MacLaren et a1.

[ METHOD FOR GENERATING A NONCONDENSIBLE GASEOUS FLUID COMPATIBLE WITH INTERHALOGEN OXIDIZERS USING PHOSPHONITRILIC CHLORIDE [75] lnventors: Richard O. MacLaren, Sunnyvale; Jack D. Breazeale, Palo Alto, both of Calif.

[73] Assignee: United Aircraft Corporation, East Hartford, Conn.

[22] Filed: May 25, 1971 [21] Appl. No.: 111,200

[52] U.S. C1 60/220, 60/207, 60/219,

, 149/109 [51] Int. Cl C06d 5/10 [58] Field of Search 60/211, 212, 213,

[4 oct. 16,1973

[56] References Cited UNITED STATES PATENTS 3,103,782 9/1963 Olah et a1. 60/219 Primary ExaminerBenjamin R. Padgett Attorney-Steven 1 Stone [5 7] ABSTRACT 7 Claims, No Drawings 1 METHOD FOR GENERATING A NONCONDENSIBLE GASEOUS FLUID COMPATIBLE WITH INTERHALOGEN OXIDIZERS USING PHOSPI-IONITRILIC CHLORIDE BACKGROUND OF THE INVENTION Conventional rocket motor systems employ liquid components as the oxidizer, fuel or, in some instances, as a monopropellant. When a liquid component is used in a rocket motor, some means must be found to pressurize the liquid to a point sufficient to cause it to flow into the combustion chamber of the rocket motor. In large rocket motors, such as large liquid propellant boosters in which a vertical orientation of the system is maintained, main tank injection is utilized whereby a pressurized gas is introduced into the ullage space in the liquid container above the level of the liquid. In tactical missiles in which the orientation of the motor is not fixed and in systems which may have to operate in a no-gravity condition, it is known to the art to employ positive expulsion devices to feed the fluid to the combustion chamber. Such devices forcibly expell the fluid by means, for example, of a collapsing or expanding bladder or a piston type arrangement in which the bladder or the piston is actuated by a pressurized gas to positively expel] the liquid contents of a tank. When conventional fuels and oxidizers are employed, the requirements on the pressurized gas are not particularly stringent and relatively inert gases, such as nitrogen, or the combustion products produced by the burning of a conventional solid propellant can be used. Nitrogen bottles and convenitonal gas generators, however, are not suitable for use in advanced tactical systems which employ highly reactive liquid oxidizers in the form of interhalogen compounds, such as for example, chlorine trifluoride, chlorine pentafluoride, and bromine pentafluoride and which have operational requirements over temperature ranges from -65 to l60 F at chamber pressures in excess of 1,000 2,000 psi. In such systems the combustion products of conventional gas generators are not suitable since they contain substantial amounts of hydrogen and carbon monoxide which could react catastrophically with the oxidizer in main tank injection or in the event leaks occur in positive expulsion devices. Further, if the oxidizer for the gas generator is the same as the interhalogen oxidizer for the main propulsion system, the use of hydrocarbon based fuels for the gas generator results in the production of substantial amounts of hydrogen fluoride (HF). HF is condensible at the temperatures and pressures encountered in the propulsion systems and also is soluble in the liquid interhalogen oxidizers. Substituting a fully halogenated polymer such as teflon for the hydrocarbon polymers is not satisfactory since such materials are not hypergolic with interhalogen oxidizers. Other compounds which should be avoided in a gas generator combustion products are various compounds of oxygen which may react vigorously or as in the case of water explosively when contacted by an interhalogen compound. Nitrogen is not suitable for use in a tactical missile due to the problems inherent in the handling of large amounts of highly pressurized gas.

According to this invention, a gas generator is pro vided which utilizes a perhalogenated oxidizer to produce combustion products which are nonreactive with interhalogen oxidizers and are primarily noncondensible gases at the conditions of operation. If the gas generator system is operated as a hybrid in which the solid gas generator fuel is reacted with a liquid interhalogen oxidizer, a hypergolic system is obtained thereby obviating any need for an ignition system. A self-sustaining solid propellant composition consisting of the mixture of solid perhalogenated oxidizing compounds in the fuel can also be fabricated.

It is accordingly an object of this invention to provide a method for generating combustion products which are nonreactive and noncondensible with liquid interhalogen compounds.

It is another object of this invention to provide a method for pressurizing a tank containing liquid interhalogen compounds.

It is a further object of this invention to provide a gas generator composition.

These and other objects of the invention will be readily apparent from the following description.

DESCRIPTION OF THE INVENTION phosphonitrilic chloride (PNCI is described in US. Pat. No. 2,872,283. As disclosed therein and in US. Pat. No. 2,788,286, phosphonitrilic chloride polymerizes quite readily and the high molecular weight polymers are rubbery materials insoluble in benzene. Polyphosphonitrilic chlorides are well known commercially available materials and the rubbery polymers exhibit elastomeric properties at temperatures as low as 65 F.

These rubbery polymers, at high temperatures, tend to depolymerize to the trimer and tetramer rather than melt, thus making these materials particularly suitable for use as a hybrid fuel in a gas generator system employing a solid fuel and a liquid oxidizer. Further, we have discovered that polyphosphonitrilic chloride is hypergolic, i.e., spontaneously ignitable, with liquid interhalogen compounds and solid perhalogenated compounds. As used herein, the term perhalogenated oxidizing agents defines perhalogenated compounds containing an oxidatively reactive halogen atom and includes the true interhalogen compounds consisting only of two or more halogens, such as for example, ClF CIF BrF and BrF salts having perhalogenated interhalogen anion such as KBrF,, Ba(BrF NOBrF,, KIF CsClF CsBRF KClF,, KBrF perhalogenated metal halide-based solids such as CIF SbF BrF SbF NOAs F NOSbF NO BF NOBF NOPF NO- AsF NO SbF NO PF and perhalogenated complexed solid oxidizers such as Mg(ClO 2 NOF, and LiClO NOF.

When polyphosphonitrilic chloride reacts with a liquid interhalogen compound such as chlorine trifluoride, combustion products consisting essentially of noncondensible gases which are nonreactive with liquid interhalogen compounds are produced according to the following reaction:

The above reaction yields about 25 moles of gas per pound of fuel. The combustion products produced by the above reaction are extremely hot and are preferably cooled to a lower temperature prior to use as a pressurizing agent. In order to accomplish this, additional liquid interhalogen is introduced into the combustion products and decomposes to cause an increase in the number of moles of gas per pound of fuel obtained to approximately 97 according to the following formula:

The additional ClF can be introduced directly into the combustion chamber or may be introduced downstream therefrom or, in main tank injection the (PNCl may be introduced directly into the main tank of liquid interhalogen oxidizer.

In the foregoing reaction, chlorine trifluoride was selected as a representative liquid interhalogen compound, however, it should be noted that other liquid interhalogen compounds such as chlorine pentafluoridc and bromine trifluoride, bromine pentafluoride, for example, may be substituted for the chlorine trifluoride as all of these materials exhibit hypergolicity with phosphonitrilic chloride. The preceding discussion involves a solid grain of polyphosphonitrilic chloride which is burned with a liquid interhalogen compound to produce the desired combustion products in a typical hybrid gas generator apparatus. It is also possible if it is desired to eliminate the need for separate fluid flow control systems for supplying the oxidizer to the gas generator to form a solid propellant from polyphosphonitrilic chloride.

Solid perhalogenated compounds of the type set forth above may be formed into a grain and reacted with a grain of polyphosphonitrilic chloride in a manner similar to that described in copending, coassigned U.S. Pat. application, Ser. No. 328,156, for Spontaneously lgnitable Solids" to give hypergolic ignition and combustion which provides gases according to the following representative formula:

The gases produced according to the above reactions are then directed to the situs of the liquid to be pressurized. The gases may be introduced directly into the ullage space of a tank of liquid interhalogen compound when main tank injection techniques are employed or may be used to pressurize the expelling element of a positive expulsion device. When so used, the gases are noncondensible at temperatures as low as -65 F and pressures as high as 2,000 psi although some of the combustion products such as ClF and fluorine are soluble to some extent in other interhalogen compounds. This solubility tends to somewhat reduce the total gas volume when main tank injection is employed, but none of the products are reactive per se with liquid interhalogen compounds and the danger of a catastrophic explosion is completely eliminated. While the invention has been described with respect to several embodiments thereof, the invention is not limited thereto. Various modifications will occur to workers skilled in the art which may be made without departing from the scope of the invention which is limited only by the following claims wherein:

We claim:

1. A method for generating gaseous combustion products which comprises burning polyphosphonitrilic chloride with a perhalogenated oxidizing agent.

2. The method of claim 1 wherein said perhalogenated oxidizing agent is selected from the group consisting of compounds of bromine and chlorine with fluorme.

3. A method for pressurizing a container of liquid interhalogen compounds which comprises generating a pressurized gas stream by burning polyphosphonitrilic chloride with a perhalogenated oxidizing agent in a combustion chamber, exhausting said gas stream from said combustion chamber and flowing said pressurized gas stream into pressure transmitting relationship with a mass of liquid interhalogen compound in a container therefor.

4. The process of claim 3 wherein the combustion products are mixed with an excess of a fluid interhalogen compound to reduce the temperature of the combustion products prior to the pressurization of said mass of liquid interhalogen compound.

5. The process of claim 3 wherein said perhalogenated oxidizing agent is selected from the group consisting of compounds of bromine and chlorine with fluorme.

6. The process of claim 4 wherein said perhalogenated oxidizing agent is selected from the group consisting of compounds of bromine and chlorine with fluo- 7. The method of claim 1 wherein said oxidizing agent is selected from the group consisting of KBrF Ba(BrF.,) NOBrF KIF CsClF CsBrF KClF KBrF ClF SbF BrF SbF NOAs F NOSbF NO BF NOBF NOPF NOZASFG, NO SbF NO PF Mg(ClO 2 NOF, and LiClO4. NOF. 

2. The method of claim 1 wherein said perhalogenated oxidizing agent is selected from the group consisting of compounds of bromine and chlorine with fluorine.
 3. A method for pressurizing a container of liquid interhalogen compounds which comprises generating a pressurized gas stream by burning polyphosphonitrilic chloride with a perhalogenated oxidizing agent in a combustion chamber, exhausting said gas stream from said combustion chamber and flowing said pressurized gas stream into pressure transmitting relationship with a mass of liquid interhalogen compound in a container therefor.
 4. The process of claim 3 wherein the combustion products are mixed with an excess of a fluid interhalogen compound to reduce the temperature of the combustion products prior to the pressurization of said mass of liquid interhalogen compound.
 5. The process of claim 3 wherein said perhalogenated oxidizing agent Is selected from the group consisting of compounds of bromine and chlorine with fluorine.
 6. The process of claim 4 wherein said perhalogenated oxidizing agent is selected from the group consisting of compounds of bromine and chlorine with fluorine.
 7. The method of claim 1 wherein said oxidizing agent is selected from the group consisting of KBrF4, Ba(BrF4)2, NOBrF4, KIF6, CsClF4, CsBrF6, KClF4, KBrF6, ClF2SbF6, BrF2SbF6, NOAs F6, NOSbF6, NO2BF4, NOBF4, NOPF6, NO2AsF6, NO2SbF6, NO2PF6, Mg(ClO4)2. 2 NOF, and LiClO4. NOF. 